Weak-held complexes

From the point of view of solute interaction with the structure of the surface, it is now very complex indeed. In contrast to the less polar or dispersive solvents, the character of the interactive surface will be modified dramatically as the concentration of the polar solvent ranges from 0 to l%w/v. However, above l%w/v, the surface will be modified more subtly, allowing a more controlled adjustment of the interactive nature of the surface It would appear that multi-layer adsorption would also be feasible. For example, the second layer of ethyl acetate might have an absorbed layer of the dispersive solvent n-heptane on it. However, any subsequent solvent layers that may be generated will be situated further and further from the silica surface and are likely to be very weakly held and sparse in nature. Under such circumstances their presence, if in fact real, may have little impact on solute retention. 

What is the coordination number of cobalt and nickel in the am-mines What type of complexes (strong-held or weak-held) do they belong to What type of orbital hybridization occurs in the formation of these complexes What spatial conhguration does this correspond to ... 

Neutral Lewis bases were removed by contacting the acid- and base-free bitumen with ferric chloride/Attapulgus clay in a column system. Weakly adsorbed complexes were desorbed with 1,2-dichloroethane while strongly held complexes were desorbed with benzene and methanol. This procedure provided two neutral Lewis bases fractions for analysis. 

The slow and incomplete retraction of the solutions containing n-propylamine is attributed in part to the presence of weakly-held polysiloxane material on an underlying, more coherent film. The fact that the solution retracts at a low contact angle (about 20° to 30°) cannot completely explain the inordinately slow retraction. It is more likely that a loose, gel-like polymeric structure impedes and in some instances prevents the withdrawal of the retracting liquid. When retraction failed to occur, the residual solution was easily displaced by water. Undoubtedly, this displacement is a complex process of desorption, liquid-liquid displacement and hydrolysis of the polymer film. 

The meaning of the terms low or high spin as applied to transition metal complexes and the terms strong or weak held as applied to ligands... 

The sorption of uranium from acid sulfate leach liquors by strong base anion exchange resins is unusual since complexes of the type [U02(S04) ] " may be sorbed by both ion exchange and addition mechanisms. High concentrations of other species are present in the leach solution due to dissolution of pyritic and siliceous components of the ore, but, apart from iron, they do not interfere with the sorption of uranium as a complex anion. Iron(III) also forms an anionic sulfate complex, but is only weakly held by the resin and is displaced ahead of the uranium. The sorption of uranium may be represented by equations of the type ... 

For iron(IlI)-porphyrinato complexes, strong-held ligands lead to low-spin (5 = 2) complexes. A pair of identical weak-held ligands, such as tetrahydro-furan, leads to intermediate-spin (5 = ) species. Five-coordinate species are, with few exceptions, high-spin (5 = f), with all hve 3d electrons in separate orbitals. Spin equilibria 5 = i 5 = f and 5 = 15 = i are not unusual. Specihc examples of these spin systems are given in Table 4.4. Higher oxidation states are found in some other hemoproteins. Fe(V)-porphyrin systems actually occur as Fe(IV)-porphyrin cation radical species, and Fe(I)-porphyrin systems exist as Fe(II)-porphyrin anion radical species. 

Relations between coordination chemistry of single metal atoms and surface chemistry are illustrated by the interaction of H2 with either a Ru atom or a Ru02(l 10) single-crystal surface [26]. As shown in Fig. 1.6, H2 forms weakly held Ti -H2 complexes with transition metal atoms [27], while on Ru02(l 10) the H2 molecule is held in a similar way above the Ru atoms, where bond lengths, vibrational frequencies, and bond strengths are quite similar in both cases. However, the further reactivity is different While with the complex compound, dissociation of the... 

Most group A metal ions have the electronic configuration of the rare gases, and the interaction of the metal with a ligand is primarily electrostatic in nature. Because the charge density (oc charge radius) is small, the water molecules are weakly held and the rate of their loss is comparable with the diffusion-controlled value of around 10 —10 s. The complex formation rate-constant for an ion in this group is therefore approximately equal to the maximum possible value, unless chelation steps are important, and the stability of the complex is reflected in the dissociation rate constant. 

At this point we have considered the interaction of oxygen with metal complexes in solution and have presented ways in which coordinated dioxygen is transferred to substrates which may themselves be coordinated to the metal. In several instances we have seen that the oxidized substrate leaves the coordination sphere. For catalysis to occur this is a necessary step. Thus, those substrates which on oxidation become more weakly held ligands, can be displaced by more unoxidized substrate and a catalytic cycle, equation (58), is possible. If, on the other hand, the oxidized substrate is more strongly held than the original substrate, catalysis does not occur. 

Complexes of weakly-held ligands can be favoured by increasing the size of PR3. The reaction ... 

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